The market has required smaller, thinner, and even lighter electronic and electric parts. Various materials have begun to be used to fabricate these parts.
Photoelectric conversion devices such as solar cells also show such a tendency, and devices of various specifications have been proposed. Among others, thin and light devices using a substrate made of a flexible organic or metal film have attracted attention because of the possibility of application to other electrical appliances and industrial machines.
Of photoelectric conversion devices using these flexible substrates, photoelectric conversion devices employing substrates made of organic materials have attracted attention because of their cost, characteristics, and workability. Photoelectric conversion devices of this type have begun to become the mainstream of photoelectric conversion devices having flexible substrates. Flexible substrates made of organic materials have numerous advantages of having high workability and being light in weight over substrates made of thin metal materials.
The structure of a photoelectric conversion device using a flexible substrate made of such an organic material is diagrammatically shown in FIG. 7, where three photoelectric elements are connected in series on a flexible substrate 1 to form an integrated photoelectric conversion device. Each of the photoelectric elements comprises a first electrode 71, a semiconductor layer 72 consisting of a non-single crystal, and second electrodes 73, 74. In this example, light impinges on the second electrodes. Therefore, one second electrode 73 is made of an ITO that is a transparent electrode material. The other second electrodes 74 are grid-like auxiliary electrodes. The second electrodes 74 are connected with the first electrodes 71 of adjacent photoelectric conversion elements. The elements are connected in series. The output from this photoelectric conversion device is developed between copper leads 75 which are soldered to the second electrodes.
Substrates having poor thermal resistance such as the aforementioned flexible substrates made of organic materials are not sufficiently resistant to heat compared with substrates made of other materials. Polyimide film which is said to be resistant to heat can withstand high temperatures of about 300 to 350° C. at best. For this reason, when photoelectric conversion devices are manufactured, application of heat is avoided as fully as possible. This method has been put into practical use.
However, after a photoelectric conversion device is fabricated, output leads must be provided to permit the use of the device. The output leads are connected with the second electrodes normally by soldering. To fuse the solder, it is necessary to apply heat locally.
Consequently, excessive heat is applied to only a part of the organic material of the flexible substrate. As a result, only this part deforms thermally. If the leads are bonded to the electrodes of the photoelectric conversion device at a temperature at which no thermal deformation takes place, then a sufficient bonding strength cannot be obtained. Under this condition, the electrical conduction deteriorates, or the bonded portions peel off, thus impairing the reliability. Hence, it is desired to improve these output leads.
Where a photoelectric conversion device is fabricated from such a flexible material by the prior art techniques, handling of the substrate has posed problems. Especially, where a semiconductor coating or the like is formed by chemical vapor deposition or other similar method, the flexibility of the substrate presents problems. Therefore, when such a substrate is used, the production facility has been required to have a special means for holding the substrate, unlike the case in which other solid substrates are employed.
A so-called roll-to-roll method has been generally accepted as a method of holding the substrate. This method begins with pulling out a flexible substrate from a roll. The substrate is fed into a plasma processing apparatus or plasma processing chamber, where the substrate is processed. Then, the substrate is rewound into a roll.
In the case of a plasma processing machine making use of the conventional roll-to-roll method, a substrate is placed substantially parallel to electric discharge electrodes located in a region where plasma processing is performed. The substrate is slowly and continuously supplied from the roll and passed through the processing region to treat the substrate with a plasma.
One example of this machine is disclosed in Japanese Patent Laid-Open No. 34668/1984. This disclosed machine is designed to form a film. The reaction chamber of this machine and its vicinities are schematically shown in FIG. 9, where a flexible substrate 201 is wound into a roll 220. The substrate is continuously fed into the reaction chamber, 221, from the roll 220. A pair of parallel-plate electrodes 222, 223, a reactive gas supply system 225, and an exhaust system 226 are mounted inside the reaction chamber 221. The continuous flexible substrate 201 passes over or by the cathode of the parallel-plate electrodes substantially parallel to them. In this structure, a film is formed on the substrate. The substrate may also be positioned on the side of the anode and processed. The substrate 201 supplied in this way is treated with a plasma while passing through the processing region close to the electrodes. That is, the substrate is treated with a plasma or a film is formed while the substrate stays in the processing region.
In the known plasma processing machine described above, a set of discharge electrodes can treat only one roll of substrate. Hence, the throughput of the plasma processing is low. In the case of silicon of a non-single crystal used for photoelectric conversion device, a film is grown at a rate within a range from 0.1 to 10 Å/sec to secure the required semiconductor characteristics, i.e., to prevent the film quality from deteriorating. It is usually necessary that a semiconductor film of a photoelectric conversion device have a thickness of about 0.3 to 2 μm. Therefore, the substrate must stay in the processing region for a long time. In consequence, the plasma processing region, or the electrodes, must be made long, or the substrate must be passed through the region at a quite low speed.
Where the electrodes are made long, the dimensions of the reaction chamber are increased. That is, the plasma processing machine occupies a large area. This is a heavy burden on mass production. If the substrate conveyance speed is decreased, the throughput of the plasma processing drops, thus hindering mass production. More specifically, in the case of the above-described semiconductor consisting of a non-single crystal, if a film 1 μm thick should be formed within a reaction chamber about 1 m long at a deposition rate of 1 Å/sec, then the substrate is transported at 0.1 mm/sec. If a roll having a length of 100 m is treated, as long as about 278 hours are required.
Consequently, there is a demand for a machine which relies on the roll-to-roll method and treats substrates at a higher speed or improves the throughput of the machine. Whether electronic devices using flexible substrates can be mass-produced or not depends heavily on this point.